The long-term objective of the proposed research is to test the hypothesis that genetic or acquired defects in the regulation of C2 gene expression contribute to the pathogenesis of systemic lupus erythematosus (SLE) and other immune complex diseases. This hypothesis is based on clinical observations indicating that individuals with complement deficiencies develop SLE and other autoimmune diseases and that, conversely, patients with these disorders frequently have low serum complement levels. To fulfill our objective we propose to first investigate the regulation of C2 gene expression in healthy individuals and then seek abnormalities in patients with SLE. Specifically, we will pursue the following aims: 1) Investigate the regulation of C2 gene expression at the level of translation. Experiments under this aim will delineate the tissue- and stimulus-specific expression of alternative forms of C2 mRNA by using RNAase protection assays. They will also define structural elements in the 5' untranslated region of C2 mRNA that are responsible for inhibiting the translational efficiency of C2. Expression of mutant C2 cDNA in mammalian cells and cell-free translation of mRNA will be utilized. 2) Investigate the regulation of C2 gene expression at the level of transcription. The C2 gene will be cloned and its exon/intron structure defined. In addition, cis-acting regulatory elements will be identified and characterized by using DNA footprinting and expression of CAT gene fusion hybrids. 3) Investigate possible defects in regulation of C2 gene expression in SLE and other immune complex diseases. These experiments will compare tissue- and stimulus-specific expression of alternative C2 mRNA forms in healthy individuals and SLE patients. They will also seek the presence of single- base mutations within cis-acting regulatory elements of C2 genes from SLE patients.